Prototype tool for creating links to POSIX DDM files in User Storage (2)

User software in science platform containers that can only read data from a file system obtains read-only random access to a data file in DDM storage without staging (copying the whole file ahead of time). Permissions enforced. Suggest rewording: Science users will benefit from being able to link to existing replicas of data products at a particular SRC site rather than requiring to download data products from the data lake into user storage (this is currently the case for Storage Inventory and the Cavern user storage). Whilst this is functional, it means that unnecessary replicas are made of data products, which would be undesirable for large and popular data products. If we can instead implement a way that user tools (e.g., but not limited to CANFAR science platform) handle links to these files whilst retaining correct permissions settings we can avoid duplication of data products into user storage.